Sphagnum's coup de grace: Carbon flow to acetate in northern peatlands
Abstract
Isotopic estimates of the microbial pathway of methane formation in acidic northern peatlands conclude that methane is derived from the pathway of CO2 reduction, whereas, microbial incubation and genomic studies have identified an important role played by acetoclastic methanogens in similar acidic systems. We believe our first ever intramolecular acetate isotopic analyses from an acidic wetland in central Pennsylvania resolve the apparent conflicting pathway estimates by indicating that the isotopic and microbial incubation studies are consistent with each other and with a pathway of methane formation through acetate from an isotopically depleted autotrophic acetate source. Intramolecular acetate isotopic measurements allow us to estimate that as much as 1/3 of the acetate in acidic wetlands is derived from autotrophy. Given a simple case of glucose fermentation to acetate, carbon dioxide, and hydrogen, our acetate production pathway estimate requires that nearly all of the carbon products from fermentation must flow through the acetate pool. Our work confirms the prior hypothesis and prior observations that acetate is an important metabolic end product in northern acidic wetlands. Further, we hypothesize an alternative fate of acetate in peat porewaters that alludes to an ecological role of autotorophic acetogens and acetate oxidizers in creating the impermeable humified peat catotelm unique to sphagnum dominated systems. The diversion of carbon flow to from methane to acetate increases the organic acid production and we hypothesize that the net transport of dissolved fulvic acids into the catotelm allows coupled acetate oxidation and fulvic acid reduction. This process of acetate consumption would create a net addition of hydrophobic, amorphous, and therefore more impermeable organic carbon. We conclude that an ecological strategy of the sphagnum mosses may not simply be to decrease the pH of the environment to slow metabolism, but rather to force the microbial community in the catotelm toward the oxidation of acetate and the reduction of peat humus, thereby aiding production of the characteristic impermeable organic seal. The sensitivity of sphagnum ecosystems to external sources of alkalinity may prove to be an important control on the ancient flux of methane from peatlands and may be an important direction of continued research.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B13A0431T
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0793;
- 1615;
- 4805;
- 4912);
- 0428 Carbon cycling (4806);
- 0434 Data sets